This invention relates to foldable mattress supports such as those used in sofa sleeper mechanisms wherein a mattress is supported on a flexible deck which is surrounded by and connected to a foldable frame.
When such a mechanism is operated to fold the frame to its seating position, there is an inherent relaxation in the longitudinal tension applied to the deck by the frame, especially near the longitudinal centerline of the deck. In units where the mattress has a generally upright portion which supports the sofa cushions in a seating configuration, this loss in deck tension reduces the amount of support the mattress is able to give to the sofa cushions. Further, when such units are in their horizontal sleeping positions, there is a natural tendency toward sagging or hammocking, particularly near the center of the bed.
This invention addresses the problem of reduced back support for sofa cushions and the problem of hammocking by providing the frame with a novel spring arrangement.